Non-Covered Loans and Allowance for Non-Covered Loan Losses - TDRs (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 item	Sep. 30, 2016 item	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($) item
AB Note | Minimum | PlainsCapital
TDRs, Non-covered loans
Number of loans into which a single loan is reconfigured | item			2
Noncovered
TDRs, Non-covered loans
Number of TDR loans granted | item	0	0
Noncovered | Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted | item			3	1
TDR at extension			$ 3,493	$ 1,196
Total Modifications			$ 3,246	$ 944
Number of TDRs granted in preceding twelve months for which payment was at least 30 days past due | item			1	1
TDR modifications, in which a payment was at least 30 days past due			$ 1,481	$ 1,196
TDR with payment at least 30 days past due			$ 1,385	$ 944
Noncovered | Secured | Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted | item			1	1
TDR at extension			$ 1,357	$ 1,196
Total Modifications			$ 1,235	$ 944
Number of TDRs granted in preceding twelve months for which payment was at least 30 days past due | item				1
TDR modifications, in which a payment was at least 30 days past due				$ 1,196
TDR with payment at least 30 days past due				$ 944
Noncovered | Secured by Commercial Properties | Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted | item			1
TDR at extension			$ 1,481
Total Modifications			$ 1,385
Number of TDRs granted in preceding twelve months for which payment was at least 30 days past due | item			1
TDR modifications, in which a payment was at least 30 days past due			$ 1,481
TDR with payment at least 30 days past due			$ 1,385
Noncovered | Commercial construction loans and land development | Payment Term Extension
TDRs, Non-covered loans
Number of TDR loans granted | item			1
TDR at extension			$ 655
Total Modifications			$ 626